21.9 Autonomic Control of Heart Rate

• • The pacemaker cells of the SA node determine the intrinsic heart rate, which is modified by the sympathetic and parasympathetic divisions of the autonomic nervous system.
• Sympathetic and parasympathetic divisions of the autonomic nervous system (ANS) innervate the heart through the cardiac plexus
• Both sympathetic and parasympathetic divisions of the ANS innervate the SA and AV nodes
• Effects of NE and ACh

  • NE release increases heart rate and contraction force by stimulating the beta receptors on nodal cells and contractile cells
  • ACh release decreases heart rate and contraction force by stimulating the muscarinic receptors on nodal cells and contractile cells
• The cardiac centers of the medulla oblongata contain the ANS centers for cardiac control
• Stimulation of the cardioacceleratory center activates sympathetic neurons; the nearby cardioinhibitory center activiates parasympathetic neurons
• SUMMARY

  • Basic heart rate is established by pacemaker cells, but it can be modified by the ANS. Norepinephrine produces an increase in heart rate and force of contraction, while acetylcholine produces a decrease in heart rate and contraction strength
  • Cardioacceleratory center in medulla oblongata activates sympathetic neurons; the cardioinhibitory center governs the activities of the parasympathetic neurons. The cardiac centers receive inputs from higher centers and from receptors monitoring blood pressure and the concentrations of dissolved gases in the blood